The digital section state machine

The digital section is modeled as a state machine with inputs and outputs in terms of INFOs at the T reference point and FEs at the V1 reference point, as well as events relating to the digital transmission system.

Table K.2 is the state transition table for the digital section. Three categories of operations procedures and corresponding states are described:

a) DS 1.x states supporting activation of the digital section for basic call control procedures and supporting initial activation of the digital section;

b) DS 2.x states supporting procedures to control loopbacks;

c) DS 3.x states supporting optionsl procedures to control the configuration of the digital section by partial activation (U-only turn-on).

The following information describes the states found in the state transition table:

K.5.6.1 State DS 1.0 (U & T deactivated)

The digital section is in its non-operational mode. INFO 0 is sent to the TE and FE6 is sent to the ET. Viewed from the user side of reference point T, the network is in state G1 according to table 4 of ANSI T1.605.

K.5.6.2 State DS 1.1 (full activation initiated)

Total activation of the digital section has been requested either by the ET sending FE1 or by the TE sending INFO 1. The first stage of activation, namely activation of the digital transmission system has been initiated. INFO 0 is sent to the TE and FE2 is sent to the ET. Viewed from the user side of reference point T, the network is in state G1 according to table 4 of ANSI T1.605.

K.5.6.3 State DS 1.2 (full activation: U sync LT→→NT)

In this second state of digital section activation, the NT has been synchronized with the LT (T6 in figure 17). INFO 2 is sent to the TE and FE2 is sent to the ET while awaiting synchronization of the LT with the

NT. Viewed form the end-user side of reference point T, the network is in state G2 according to table 4 of ANSI T1.605.

K.5.6.4 State DS 1.3 (full activation: U activated)

In this third stage of digital section activation, the digital section has synchronized in both directions. INFO 2 continues to be sent to the TE, but FE3 is sent to the ET while awaiting receipt of INFO 3 from the TE. Viewed from the end-user side of reference point T, the network is in state G2 according to table 4 of ANSI T1.605.

K.5.6.5 State DS 1.4 (full activation: U & T activated)

The digital section is in its stable active state, and INFO 3 has been received from the TE. FE4 is sent to the ET and INFO 4 is sent ti the TE. (See note 4 table K.2). Viewed from the end-user side of reference point T, the network is in state G3, according to table 4 of ANSI T1.605.

K.5.6.6 State DS 1.5 (full activation: LOS/LFA at T)

The signal or frame alignment has been lost at the T reference point while the digital section is in the stable active state. This may have been caused for example by the temporary disconnection of the TE. INFO 2 is sent toward reference point T to assist rapid synchronization of the TE and FE12 is sent to the ET while awaiting either the receipt of INFO 3 from the TE , or FE5 from the ET (instruction to deactivate). Viewed from the end-user side of reference point T, the network is in state G2 according to table 4 of ANSI T1.605. Upon receipt of INFO 3 from the TE, the digital section returns to state DS 1.4.

K.5.6.7 State DS 1.6 (full activation: deactivating)

The digital section has been instructed to deactivate by sending FE5 from the ET; INFO 0 is sent to the TE. Viewed from the end-user side of reference point T, the network is in state G4 according to table 4 of ANSI T1.605. Upon receipt of INFO 0 from the TE, the deactivation of the digital section, or expiry of timer T2, the digital section changes to state DS 1.0.

K.5.6.8 State DS 1.7 (network defect)

LOS/LFA has occurred on the transmission system, or power has been lost at the NT. The defect condition is reported to the ET by sending FE7. the INFO sent to the TE shall depend on the NT state prior to the defect condition. Upon receipt of FE5 from the ET, the digital section changes to state DS 1.0.

K.5.6.9 State DS 2.0 (loopback 1 or loopback 1a initiated)

Activation of loopback 1 or 1a has been requested by the ET by sending FE9 or FE10, respectively. Activation has been initiated and FE2 is sent to the ET.

K.5.6.10 State DS 2.1 (loopback 1 or 1a activated)

The appropriate loopback is in its stable state. FE4 is sent to the ET. The control of the NT is not part of the loopback procedure, so the INFO sent to the TE can not be defined.

K.5.6.11 State DS 2.2 (2B+D loopback initiated)

Activation of a 2B+D loopback at the NT toward the network has been requested by the ET by sending FE8. Activation has been initiated, and FE2 is sent to the ET. More details are found in annex C.

K.5.6.12 State DS 2.3 (2B+D loopback: U sync LT→→NT)

The NT has recognized the request for the 2B+D loopback. INFO 2 is sent to the TE. More details are found in annex C.

K.5.6.13 State DS 2.4 (2B+D loopback: U activated)

The NT has recognized looped back INFO 2, acting in this case as INFO3 does during normal activation FE3 is sent to the ET. More details are found in annex C.

K.5.6.14 State DS 2.5 (2B+D loopback activated)

The NT sends INFO 4 frames as described in annex C. FE4 is sent to the ET.

K.5.6.15 State DS 3.0 (partial activation (U-only) initiated)

The digital section has entered this optional state for DS 1.0 following receipt from the ET of FE11. FE2 is returned to the ET and INFO 0 is sent to the TE. Viewed from the end-user side of reference point T, the network is in state G1 according to table 4 of ANSI T1.605. The digital section remains in this state until synchronized in both directions.

K.5.6.16 State DS 3.1 (Partial activation (U-only): U activated)

The digital section is synchronized in both directions and the ET has been notified by sending FE3. This is the stable partially activated state; INFO 0 is sent to the TE. Viewed form the end-user side of reference point T, the network is in state G1, according to table 4 of ANSI T1.605.

K.5.6.17 State DS 3.2 (Partial activation (U-only): T activation request)

Activation of the interface at reference point T has been initiated either by receipt of FE1 from the ET or by receipt of INFO 1 from the TE, while the digital section is in state DS 3.1. FE2 is sent to the ET, but the digital section is already fully synchronized, and INFO 2 is sent to the TE while awaiting recieipt of INFO 3 from the TE. Viewed from the end-user side of reference point T, the network is in state G2 according to table 4 of ANSI T1.605. Upon receipt of INFO 3 from the TE, the digital section will change to state DS 3.3.

K.5.6.18 State DS 3.3 (partial activation (U-only): U & T activated)

The digital section is in the stable active state, equivalent to DS 1.4 in the normal mode of operation. INFO 3 has been received from the TE and INFO 4 returned. (See note 4 in table K.2) FE4 is sent to the ET. Viewed from the end-user side of reference point T, the network is in state G3 according to table 4 of ANSI T1.605.

K.5.6.19 State DS 3.4 (partial activation (U-only): LOS/LFA at T)

This state is equivalent to DS 1.5 in the normal mode of operation. The signal or frame alignment has been lost on the end-user side of reference point T while the digital section is in its stable active state. This may have been caused for example by temporary disconnection of the TE. INFO 2 is sent toward reference point T to assist rapid resynchronization of the TE, and FE12 is sent to the TE while awaiting either the receipt of INFO 3 from the TE or FE13 from the ET (instruction to deactivate the interface at reference point T). Viewed from the end-user side of reference point T, the network is in state G2 according to table 4 of ANSI T1.605. Upon receipt of INFO 3 from the TE, the digital section returns to state DS 3.3.

K.5.6.20 State DS 3.5 (partial activation (U-only): U-only request)

Deactivation of the interface at reference point T has been initiated in response to the receipt of FE13 from the ET. FE3 is returned to the ET and INFO 0 is sent to the TE. Viewed from the end-user side of reference point T, the network is sin state G4 according to table 4 of ANSI T1.605. Upon receipt of INFO 0 from the TE or expiry of timer T2, the digital section changes to state DS 3.1.